Dual-tube shock absorbers such as these are relatively well known in the prior art, cf. DE 10 2004 032 472 A1 and DE 2 257 556.
As is generally known, in dual-tube shock absorbers the working cylinder and the container tube form two chambers: The working chamber within the working cylinder in which the piston and the piston rod move, and the annular oil storage space between the working cylinder and the container tube which is used to equalize the changes in oil volume caused by the motion of the piston rod in the working chamber. The oil storage space is in one part filled with mineral oil and in the other with air which is under a pressure of six to eight bar. As the piston rod is retracted and extended, the gas pressure in the oil storage space is increased and reduced according to the exchanged oil volume. Two damping valves are used for damping: The piston valve and the bottom valve. When the vehicle rebounds, the piston valve alone assumes damping. The valve opposes resistance to the oil flowing down out of the space above the piston. The upward motion of the piston is braked. By way of an open nonreturn valve in the bottom valve, the oil, which is required in the working chamber, can flow unobstructed out of the storage space. When the vehicle suspension is compressed, the damping of the bottom valve is determined for one part also by the flow resistances of the piston in the compression direction. The oil which has been displaced by the retracting piston rod flows into the storage space. The bottom valve opposes resistance to this flow and thus brakes the motion, see “Die Bibliothek der Technik” [Library of Engineering], Vol. 185, Motor Vehicle Shock Absorbers, Peter Causemann, Verlag. Moderne Industrie, pp. 19/20.
In this connection the circumstance is especially disadvantageous that the known dual-tube shock absorbers as a result of the oscillating container tube have a relatively large unsprung mass. To simply “upend” a dual-tube shock absorber known from the prior art in order to avoid the aforementioned disadvantage is not technically possible, since in this case the bottom valve would no longer lie below the oil level, i.e., the upended dual-tube shock absorber would no longer be serviceable. Consequently, with the known dual-tube shock absorber technical implementation is not possible either, if, for example, there is the requirement, functionally or in terms of a package, that the container tube should be at relative rest and the piston rod oscillate.
The object of the invention is to develop a dual-tube shock absorber according to the type given in the preamble of claim 1 while avoiding the indicated disadvantages, such that the dual-tube shock absorber has lower unsprung masses.